1. Field of the Invention
The present invention relates generally to the field of low-noise amplifiers. In particular, the present invention relates to the development of low-noise programmable gain amplifiers (PGAs) suitable for placement on integrated circuits (ICs) and for use in signal processing applications.
2. Related Art
PGAs are used in various analog signal processing applications where an electrical signal of varying amplitude must be either amplified or attenuated before subsequent signal processing. Various gain and/or attenuation settings are required to accommodate the wide dynamic range needed for the amplifier""s input stages. Numerous conventional techniques exist for meeting these demands.
What are needed, however, are techniques for providing attenuation in closed loop amplifiers without increasing their feedback factor. What is also needed is an approach to ensure suitable start-up conditions and avoid latchup, particularly in complimentary metal oxide semiconductor (CMOS) PGAs. Finally, a technique is needed to eliminate mismatched characteristics commonly found in passive elements across IC substrates due to process gradients.
The present invention includes a PGA system having an amplifier and a first gain control mechanism with a circuit input port. The first gain control mechanism is positioned along a feedback path of the amplifier. The first gain control mechanism is configured to (i) receive an input signal and (ii) apply gain to the received input signal, the applied gains including gain values of greater than or equal to one. A second gain control mechanism is coupled to the first gain control mechanism and is integrated with a function of the PGA. The second gain control mechanism (i) provides gain values of less than one and (ii) decreases a feedback factor of the PGA when the gain values are provided having values of less than one.